The use of vacuum hot pressed intermetallic composites as self resistance heated evaporation sources is well established. These composites are employed in the evaporation of aluminum and a wide range of other metals and alloys. One class of these composites comprises binary intermetallics composed of titanium diboride (TiB.sub.2) and boron nitride (BN). Another class comprises ternary intermetallics including the above-named materials with the addition of aluminum nitride (AlN). Other intermetallics include small quantities of tungsten or calcium compounds. These composites are available in a wide range of resistivities of from about 50 to 2000.mu. .OMEGA.-cm (micro-ohm centimeter) and are usually provided with a cavity to hold the evaporant.
Prior art composites employed in evaporation processes have had a problem of maintaining a consistency of cavity wetting over the entire cycle of the composites life. A particularly critical area in this life cylce is the very beginning of the evaporation cycle where the evaporant is initially introduced to the high temperature source.